Enterococci have been recognized as being pathogenic for humans since the turn of the century when they were first described by Thiercelin in 1988 as microscopic organisms. The genus Enterococcus includes the species Enterococcus faecalis or E. faecalis which is the most common pathogen in the group, accounting for 80-90 percent of all enterococcal infections. See Lewis et al. (1990) Eur J. Clin Microbiol Infect Dis.9:111-117.
The incidence of enterococcal infections has increased in recent years and enterococci are now the second most frequently reported nosocomial pathogens. Enterococcal infection is of particular concern because of its resistance to antibiotics. Recent attention has focused on enterococci not only because of their increasing role in nosocomial infections, but also because of their remarkable and increasing resistance to antimicrobial agents. These factors are mutually reinforcing since resistance allows enterococci to survive in an environment in which antimicrobial agents are heavily used; the hospital setting provides the antibiotics which eliminate or suppress susceptible bacteria, thereby providing a selective advantage for resistant organisms, and the hospital also provides the potential for dissemination of resistant enterococci via the usual routes of hand and environmental contamination.
Antimicrobial resistance can be divided into two general types, inherent or intrinsic property and that which is acquired. The genes for intrinsic resistance, like other species characteristics, appear to reside on the chromosome. Acquired resistance results from either a mutation in the existing DNA or acquisition of new DNA. The various inherent traits expressed by enterococci include resistance to semisynthetic penicillinase-resistant penicillins, cephalosporins, low levels of aminoglycosides, and low levels of clindamycin. Examples of acquired resistance include resistance to chloramphenicol, erythromycin, high levels of clindamycin, tetracycline, high levels of aminoglycosides, penicillin by means of penicillinase, fluoroquinolones, and vancomycin. Resistance to high levels of penicillin without penicillinase and resistance to fluoroquinolones are not known to be plasmid or transposon mediated and presumably are due to mutation(s).
Although the main reservoir for enterococci in humans is the gastrointestinal tract, the bacteria can also reside in the gallbladder, urethra and vagina.
E. faecalis has emerged as an important pathogen in endocarditis, bacteremia, urinary tract infections (UTIs), intraabdominal infections, soft tissue infections, and neonatal sepsis. See Lewis et al. (1990) supra. In the 1970s and 1980s enterococci became firmly established as major nosocomial pathogens. They are now the fourth leading cause of hospital-acquired infection and the third leading cause of bacteremia in the United States. Fatality ratios for enterococcal bactermia range from 12% to 68%, with death due to enterococcal sepsis in 4 to 50% of these cases. See T. G. Emori (1993) Clin. Microbiol. Rev. 6:428-442.
The ability of enterococci to colonize the gastrointestinal tract, plus the many intrinsic and acquired resistance traits, means that these organisms, which usually seem to have relatively low intrinsic virulence, are given an excellent opportunity to become secondary invaders. Since nosocomial isolates of enterococci have displayed resistance to essentially every useful antimicrobial agent, it will likely become increasingly difficult to successfully treat and control enterococcal infections. Particularly when the various resistance genes come together in a single strain, an event almost certain to occur at some time in the future.
The etiology of diseases mediated or exacerbated by Enterococcus faecalis, involves the programmed expression of E. faecalis genes, and that characterizing these genes and their patterns of expression would dramatically add to our understanding of the organism and its host interactions. Knowledge of the E. faecalis gene and genomic organization would improve our understanding of disease etiology and lead to improved and new ways of preventing, treating and diagnosing diseases. Thus, there is a need to characterize the genome of E. faecalis and for polynucleotides of this organism.